Support » Plugin: WP Mail SMTP by WPForms » Sending via Amazon SMTP Error: Duplicate header ‘MIME-Version’

  • Resolved codingdude



    I have setup WP Mail SMTP to work with an Amazon AWS SMTP server. Sending test emails works.

    I have installed the User Verification plugin ( that should send a confirmation email when a user registers.

    But, when the user registers I get the following error:

    SMTP Error: data not accepted.SMTP server error: DATA END command failed Detail: Transaction failed: Duplicate header ‘MIME-Version’.
    SMTP code: 554

    I’m not sure when the MIME-Version header is set twice. I tried commenting out the line in that sets the MIME-Version header in the User Verification plugin, but it didn’t make any difference. Here’s how the headers look like

    [MIMEHeader:protected] => Date: Sat, 13 Jul 2019 07:54:48 +0000
    From: Admin <>
    Subject: New User Submitted –
    Message-ID: <>
    X-Mailer: WPMailSMTP/Mailer/smtp 1.5.1
    MIME-Version: 1.0
    MIME-Version: 1.0
    Content-Type: text/html; charset=ISO-8859-1

    Any idea why this happens?


Viewing 7 replies - 1 through 7 (of 7 total)
  • Plugin Support Sanjeev Aryal


    Hi John,

    Thanks for reporting the issue. This seems to be a bug within the plugin and I’ve passed this issue to our development team and we will be investigating soon.

    Have a good one!

    Can you provide an update on this issue?

    To my understanding WP Mail SMTP is supposed to overwrite/correct the headers. I have other plugins that create duplicate MIME-Version headers and AWS SES is refusing to send these as well.

    • This reply was modified 3 months, 2 weeks ago by breeakpoint.

    I have fixed the issue with the following code in my function.php

      PHPMailer inserts the below custom headers so we must remove them as it creates
      duplicate issues with AWS SES. WP potential fix of issue will come with 5.3.
    add_action('phpmailer_init', 'phpmailer_init_fix');
    function phpmailer_init_fix($mailer) {
        $headers = $mailer->getCustomHeaders();
        foreach ($headers as $key => $header) {
            if ($key !== 'MIME-Version' && $key !== 'X-Mailer' ) {
                $mailer->addCustomHeader($key, $header);
    Plugin Support Sanjeev Aryal


    Hi @breeakpoint,

    Glad to know you sorted this out! We are investigating the issue as the error occurs only on certain server configurations. Hopefully, this will get fixed soon.

    Have a good one! 🙂

    No worries, I did’nt mention it in my post but a comment in my code. It is an issue with core WordPress that should be fixed in v5.3 (but I have not confirmed if it was as I have not upgraded yet)

    Plugin Support Sanjeev Aryal


    Hi @breeakpoint,

    Thanks for the information. We are not aware of any issue with the WordPress core. Please let us know after confirmation.


Viewing 7 replies - 1 through 7 (of 7 total)
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